Conformational and electronic (AIM/NBO) study of unsubstituted A-type dimeric proanthocyanidin

The conformational space of the unsubstituted A-type dimeric proanthocyanidin was scanned using molecular dynamics at a semiempirical level, and complemented with functional density calculations. The lowest energy conformers were obtained. Electronic distributions were analysed at a higher calculation level, thus improving the basis set. A topological study based on Bader’s theory (AIM: atoms in molecules) and natural bond orbital (NBO) framework was performed. Furthermore, molecular electrostatic potential maps (MEPs) were obtained and analysed. NMR chemical shifts were calculated at ab initio level and further compared with previous experimental values; coupling constants were also calculated. The stereochemistry of the molecule is thoroughly discussed, revealing the key role that hyperconjugative interactions play in defining experimental trends. These results show the versatility of geminal spin–spin coupling ²J(C-1′,O) as a probe for stereochemical studies of proanthocyanidins.     

Detection and preliminary characterization of extracellular proteolytic activities of the haloalkaliphilic archaeon Natronococcus occultus

Extracellular proteolytic activity was detected in the haloalkaliphilic archaeon Natronococcus occultus as the culture reached the stationary growth phase. Proteolytic activity was precipitated with ethanol and subjected to a preliminary characterization. Optimal conditions for activity were attained at 60° C and 1–2 M NaCl or KCl. Gelatin zymography in the presence of 4 M betaine revealed a complex pattern of active species with apparent molecular masses ranging from 50 to 120 kDa. Experiments performed with inhibitors of the various groups of proteases indicated that the extracellular proteolytic enzymes of N. occultus are of the serine type. Individual protein species showed some differences in salt and thermal stability. Received: 10 January 1997 / Accepted: 27 June 1997     

A Procedure for Ecological Tiered Assessment of Risks (PETAR)

Several procedures for Ecological Risk Assessment (ERA) have been suggested. The use of these existing procedures often relies on availability of existing data and/or on large resources for acquisition of new ones. This paper presents a three-tiered procedure for retrospective evaluation of risks adapted to limited resources and scarce background information of relevance for risk assessments, such as in developing countries. The tiers require successively more detailed investigations. The approach assures that resources available for site-specific investigations are directed towards well-formulated questions raised during previous stages of the assessment. The first tier, the preliminary assessment, is a qualitative evaluation of existing information on anthropogenic stressors, sources of stressors and expected ecological effects. The second tier is a regional risk assessment; a semi-quantitative evaluation of ecological risks, over large geographical areas, which results in a ranking of sources and stressors having the greatest potential for ecological impact and ranking of subareas inside the study area more likely to be impacted. The final tier is a site-specific and quantitative risk assessment, at a smaller scale and requiring more resources, that incorporates methodologies for establishing causality between exposure to multiple stressors and effects on specific endpoints of ecological and societal relevance.     

Response of a continuous anaerobic culture to periodic variation of the feeding mash concentration

The authors studied the influence of periodic variations (one cycle per 24 hr) of the feeding mash concentration of a continuous anaerobic culture of Saccharomyces cerevisiae in sugarcane molasses media at constant dilution rate. It was observed that the average yield coefficients during the transient state were practically equal to the yield coefficient obtained during steady-state experiments. It was also observed, in each experiment, that the average specific growth rate during the transient state was equal to the dilution rate.     

Microsatellite markers for <Emphasis Type="Italic">Caesalpinia echinata</Emphasis> Lam. (Brazilwood), a tree that named a country

Caesalpinia echinata, commonly known as Pau-brasil (Brazilwood), the famous tree that named Brazil is native to the Atlantic forest. Men extensively exploited it ever since discovery and colonial times due to its value as a source of red dye. As a consequence, Brazilwood is a threatened species with populations reduced to small forest fragments. Ten polymorphic microsatellite loci were developed from an enriched genomic library. Using fluorescently-labeled primers, a total of 83 alleles were found after analyzing a sample of 44 trees. These high genetic information content markers should allow detailed investigations of mating systems, gene flow, population structure and paternity in natural populations.     

Protective effect of 3,5,3′-triiodothyroacetic and 3,5,3′,5′-tetraiodothyroacetic acids on serum albumin fibrillation

Inhibition or reversion of protein self-aggregation has been suggested as a possible preventive mechanism against amyloid diseases, and many efforts are underway to found out molecules capable to restrain the protein aggregation process. In this paper, the inhibitory effects of thyroid hormone analogues on heat-induced fibrillation process of serum albumin are reported. Among the analogues tested, 3,5,3′,5′-tetraiodothyroacetic and 3,5,3′-triiodothyroacetic acid showed the most important inhibitory effects on amyloid formation. Thyroxine exhibits a lesser protective effect, while 3,5,3′-triiodothyronine showed no significant inhibition. The gaining of a negative charge together with a size reduction of the hormone molecule could play an essential role in the inhibition of fibrils formation. According to infrared spectroscopy results, the thyroid hormones analogues protective effects proceed via the stabilization of the protein native structure. The current work demonstrates the effectiveness of naturally occurring molecules in the inhibition of albumin fibril formation.